Prebooking Hostels?!

Hi, I need a bit of advice really are people prebooking hostels a few nights ahead? Or just turning up as I don't know how long i will be statying in each place and sort of wanted to go with the flow but then don't want to end up without anywhere to stay?!

Depends on time of year and region. For example, for the South Island in New Zealand, booking a couple of days ahead (and week or two for private rooms) is pretty much a must from December through March. NYE in Sydney has to be booked at least half a year (but preferably 9+ months) in advance if you're even the least bit picky about where you want to stay, and gets effectively impossible around now.

Me, I always like knowing exactly where I'm going to when I arrive in a new city, so always book at least 2-3 days in advance, but generally a week or two. It helps that you generally can cancel hostels free of charge up to 24 hours in advance, so I can always opt to extend my stay somewhere and postpone the next destination. I end up hardly ever using that option, but knowing it's there means I don't feel limited when booking ahead, and gives me the big benefit of being able to thoroughly research places well ahead of time.